The Siemens 5SU9356-7KP20 is a 2-pole (1P+N) RCD-operated circuit breaker from the SENTRON 5SU9 series — an RCBO that combines overcurrent protection and residual current detection in a single 36 mm wide module. The Type A residual-current element catches pulsating DC faults (common with VFDs, LED drivers, and switched-mode supplies) as well as sinusoidal AC faults.
The 20 A rating is at 30 °C ambient; at 40 °C it derates to 18.8 A, at 45 °C to 18.2 A, at 50 °C to 17.4 A, and at 55 °C to 16.2 A. If the panel runs warm — say 45 °C inside a sealed enclosure — the breaker's effective capacity drops to 18.2 A, so size the load accordingly. The C-curve (magnetic trip at 5–10× In) means it's suited for circuits with moderate inrush, like small motors or transformers, without nuisance tripping. The Type A residual-current detection covers pulsed DC faults up to 6 mA superimposed on AC, which is the standard for equipment with single-phase rectifiers.
Mounting position is any orientation, so no restrictions on vertical or horizontal rail placement. Supply can be fed from either top or bottom, which simplifies busbar routing in crowded enclosures. IP20 rating is standard for installed distribution boards; the breaker itself is touch-protected per the product feature.